1. Field of the Invention
The present invention relates to an RF (Radio Frequency) supply system for supplying an RF power for plasma generation, and a plasma processing apparatus using the system. For example, the plasma processing apparatus is used for performing a plasma process on a target substrate in a semiconductor processing system. The term “semiconductor process” used herein includes various kinds of processes which are performed to manufacture a semiconductor device or a structure having wiring layers, electrodes, and the like to be connected to a semiconductor device, on a target substrate, such as a semiconductor wafer or a glass substrate used for an LCD (Liquid Crystal Display) or FPD (Flat Panel Display), by forming semiconductor layers, insulating layers, and conductive layers in predetermined patterns on the target substrate.
2. Description of the Related Art
In manufacturing processes for semiconductor devices or FPDs (Flat Panel Display), plasma processing apparatuses are often used for performing processes by plasma, such as etching, deposition, oxidation, and sputtering. In general, a plasma processing apparatus includes an RF electrode disposed outside or inside a process container or process chamber, and an RF supply section configured to supply an RF power to the RF electrode. Typically, the RF supply section includes not only an RF power supply for outputting the RF power, but also a matching unit for matching the impedance of the RF power supply side with the impedance of the load side (the electrode, plasma, and process chamber).
FIG. 4 is a view showing a plasma processing apparatus including a conventional RF supply section. Specifically, an upper electrode 102 and a lower electrode 104 are disposed in parallel with each other inside a process chamber 100 configured to reduce a pressure therein. A lower electrode 104 used as a worktable is disposed to place thereon a target substrate, such as semiconductor wafer W. According to this arrangement, the lower electrode 104 serves as an RF electrode, to which an RF power is supplied from the RF supply section 106. The upper electrode 102 serves as a counter electrode, which is connected to the ground potential through the process chamber 100. The space inside the process chamber 100, particularly the space between the upper electrode 102 and lower electrode 104, is supplied with a predetermined process gas from a process gas supply source (not shown). An exhaust port 108 is formed at the bottom of the process chamber 100, and is connected to an exhaust unit 112 through an exhaust line 110. A substrate transfer port (not shown) is formed in the sidewall of the process chamber 100, and is configured to be opened and closed when a substrate W is transferred in and out.
The RF supply section 106 includes an RF power supply 114, a matching unit 116, and a feed rod 118. The RF power supply 114 is configured to output an RF power with a predetermined frequency of, e.g., 13.56 MHz at a predetermined power level. For example, the matching unit 116 includes an L-type circuit consisting of two variable capacitors 120 and 122 and one coil 124. The matching unit 116 further includes a voltage/current sensor 126 (FIG. 5), a controller, and an actuator (not shown) to adjust and control the capacitances of the capacitors 120 and 122. In other words, the matching unit 116 is structured as a so-called matching box. The feed rod 118 is formed of a coaxial tube with one end connected to the output terminal of the matching unit 116, and the other end connected to the bottom of the lower electrode 104. The feed rod is used for the transmission path to reduce the transmission impedance to be as small as possible.
As described later, however, the present inventor has found some problems in the structure shown in FIG. 4. One of the problems concerns transmission loss and heat generation in supplying an RF power. Another problem concerns flexibility in the size and location of the matching unit. A further problem concerns flexibility in the design of the RF generation mechanism on the process chamber side, in accordance with increase in the diameter of the process chamber.